In oil and gas exploration and development operations, it is often desirable to remove casing which has previously been set in the wellbore. Casing removal requires that the casing string first be severed, and the free end then pulled to the surface, to remove the severed portion.
Conventional apparatus and techniques for extraction of well casing typically involve the use of multiple trips to move cutting and extracting equipment downhole. Thus, in removal operations a cutting device is first lowered into the wellbore to cut the casing at a desired depth after which time the cutting device is returned to the surface. A spearing device is then lowered inside the well and engaged to the free end of the casing. Once the free end of the casing is engaged, an attempt is then made to recover the casing by pulling, or, in the case where jars are used, by a combination of pulling and jarring. If these attempts to remove the casing are unsuccessful, the spear assembly is removed from the wellbore and the cutting device reattached to the tool string to sever the casing at a point above the original cut. The pulling/jarring process is then repeated until the casing is recovered.
Such prior art apparatuses and techniques for retrieving well casing are time consuming and costly. This time and expense is a result of the utilization of separate cutting and extraction tools, which are typically run downhole independently. Even when casing is retrieved without the need to complete a second cut of the casing, at least two trips are necessary for a complete cutting and retrieval operation. When a significant length of casing is extracted, considerable rig time must be used to move the tools downhole to the site of the cut. Time and expense are therefore increased when multiple cuts are necessary to retrieve the casing.
In certain operations, casing cutting may be required when performing slot recovery operations. During slot recovery, the object is to construct a new well with new barriers from a previously used slot while shutting off all communication with an old reservoir. Cutting and pulling casing may be restricted due to cement behind production casing or barite settling from drilling fluid in the production casing annulus. Such slot recovery operations may thus require the cutting and removal of multiple sections of casing from a wellbore. Because slot recovery operations often involve cutting a casing segment in a first trip and pulling the cut casing in a second trip, such operations are often time consuming and expensive.